1. Field of the Invention
The present invention relates to a turbo-molecular pump.
2. Description of the Related Art
A turbo-molecular pump for use in semiconductor manufacturing equipment or the like is required to have high evacuation performance and durability against high gas load. In such equipment, a hybrid-type turbo-molecular pump is used which comprises a blade (or turbine blade) pumping section disposed on an upstream side of the pump, and a thread groove pumping section disposed on a downstream side of the pump and adapted to produce an evacuation (i.e., pumping-out) function in intermediate to viscous flow regions (see, for example, JP 2005-105846A).
Typically, the thread groove pumping section comprises a cylindrical-shaped screw stator, and a rotor cylinder adapted to be rotated inside the screw stator at a high speed. The evacuation function of the thread groove pumping section can be enhanced along with an increase in length of the thread groove pumping section in an axial direction of the pump. Thus, with a view to obtaining enhanced function of the thread groove pumping section while facilitating reduction in size of the pump, the thread groove pumping section is designed such that a downstream edge thereof is extended to reach a position of a discharge port provided in a pump base, in some cases.
In cases where the downstream edge of the thread groove pumping section is extended to reach the position of the discharge port, if the rotor cylinder is broken, resulting broken pieces can fly out of the pump through the discharge port. Then, the escaped broken pieces will be sucked into a back pump (e.g., a dry pump) fluidically connected to the discharge port of the turbo-molecular pump, and likely to lead to failures of the back pump.